Method for obtaining calibration data

ABSTRACT

A method for obtaining data for calibrating a recording system in situ. The recording system has a plurality of channels, each having a sensing element, a transmitting element, and a recording element. In the method, the sensing and transmitting elements are installed in a preselected position, the sensing elements are controllably excited, a signal representative of the magnitude of excitation relative to time is delivered from each sensing element, separately received, corrected in response to the sensitivity of its respective channel, composited one with the other to form a composite signal, and a systems calibration&#39;&#39;s operator is computed for each of the channels from the composite signal.

Unite States Patet Tims Sept. 2, 1975 METHOD FOR OBTAINING CALIBRATION Published 5-18-43.

DATA

75 Inventor: Harold A. Tims, Bartlesville, Okla. f

ASSISHIHI ExammerT. M. Blum [73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla. 57] ABSTRACT [22] Filed: Jan. 29', 1973 A method for obtaining data for calibrating a record- [21 1 Appl 327,732 ing system in situ. The recording system has a plurality of channels, each having a sensing element, a transmitting element, and a recording element. In the [52] US. Cl. 340/155 MC; 340/l5.5 CC method the Sensing and transmitting elements are [51] Int. Cl G01v 1/00 Stalled in a preselected position, the sensing elements [58] Field of Search 340/155 17 are controllably excited, a signal representative of the magnitude of excitation relative to time is delivered [56] References Cited from each sensing element, separately received, cor- UNITED STATES PATENTS rected in response to the sensitivity of its respective 2,087,702 7/1937 Peters 340/155 MC channel, Composited one with the other to form 8 2,265,538 12/1941 Minton... 340/ 15.5 GC composite signal, and a systems calibrations operator 3,406,781 10/1968 Willner 340/17 is computed for each of the channels from the com- OTHER PUBLICATIONS A.P.C. Application of Maillet, Serial No. 254,743

posite signal.

9 Claims, 1 Drawing Figure 1 1 1 I I l H T SENSING TRANSMITTING RECORDING r ELEMENT No.1 ELEMENT NO, I ELEMENT No.1 L l I "1 Q1 SYSTEM CALIBRATION, I 5 6 7 OPERATOR COMPUTATION 2 l 2 2 A 1 T2 SENSING TRANSMITTING RECORDING r1 I ELEMENT No.2 ELEMENT Noa ELEMENT N042 l K 9 3 2 l 10 STATIC 2 cuRRENT SYSTEM CALIBRATlON SOURCE L OPERATOR coMRuTATmN EIN [6N F 7 CA SENSING TRANSMITTING 0 1; RECORDING TN ELEMENT NoN ELEMENT No.N ELEMENT No.N l x N Q 1 SYSTEM CALlBRATION' N OPERATOR COMPUTATION I -w Z G] METHOD FOR OBTAINING CALIBRATION DATA In recording systems having a plurality of channels each having a sensing element, a transmitting element, and a recording element, the sensitivity of each channel sometimes varies. This variation in channel sensitivity can be caused by several, factors such as differences in sensing elements 'and construction, differences in cable length between the" sensing element and the recording element, differences in cable construction, atmospheric conditions, differences in ages of the equipment'among otherS fof example.

It is therefore desirable to provide a method for obtaining data for calibrating a recording system in situ for subsequent calibrating the system and thereby obtaining recordings of improved accuracy. An example use of the method of this invention would be for obtaining data for calibrating a seismic recording system utilized in the oil industry.

This invention, therefore, resides in a method for obtaining data for calibrating a recording system in situ. The recording system has a plurality of channels, each having a sensing element, a transr'nitting"element, and a recording element. In the method, the sensingelements and transmitting elements are installedin a preselected position, the sensing elements are controllably excited, a signal representative of the magnitude of excitation relative to time is delivered from each sensing element, separately received, corrected in response to the sensitivity of its respective sensing elements, composited one with the other to form a composite signal and a .systems calibration operator iscomputed for each of the channels from the composite signal.

The method of this invention-willbe described with reference to aiseismic recording system such as utilized in the oilindustry. It should be understood, however, that the method can be used with other. recording-sys tems. '1" '5 The method of this invention, sensing elements, for example, geophones, and transmitting elements including the cable to each geophone are installed in a preselected position. This position is preferably the array of the geophones which will subsequently be utilized for a recording of-the subsequent formations at this location. These preselected positions are r'n any and varied and are known in the art. I I r r With the sensing and transmitting elementsselectively positioned, each of the sensing elemer its is cofi troll'ably excited, and a signal representative ofthe magnitude of excitation relative to time is delivered to and separately received by the recording element.

Where the sensing elements are gcophones having a suspended mass, for example, the geophoncs can be controllably excited for example by substantially simultaneously biasing the suspended mass of each of the geophones for a preselected period of time and thereafter substantially, simultaneously, releasing eachrn'ass. In gcophones of this construction the mass can be biased by passing a static current toeach g eophone. 'Release of the suspended mass can bc accomplished by terminating the current passing through each geophone. The release of the suspended mass will thereby cause the sensing element to be controllably "excited and the signal to be delivered as described above.

In the drawing, the sole FIGURE is a schematic rep resentation of a system utilizing the method of the invention.

- Referring to the FIGUREin detail, thereis illustrated a system having a plurality of channels each having a sensing element 5 5 3.15 a transmitting element 6,, 6 6 and a recording-element 7,, 7 7 A'means for controllablyexciting each sensing element 5 5 5,, 'comprises a static current source 9"and'means 10 for terminating the current passing through each sensing element.

Each received signal K is thereafter corrected by multiplying each separate signal (K,-) by a constant (0,) which is representative of the sensitivity of the sensing element producing the respective signals for obtaining a corrected signal ((1,) for each channel.

Each of the corrected signals 6 are thereafter composited to form a composite signal. The corrected signals can be composited with respect to time or with respect to frequency.

The corrected signals (G,-) can be composited with respectto time by the equation: I

where: l U l I A (l) the composite signal in the time domain;

N thetotal number of'channels; i

j a channel number; v

G -(t) corrected signal in time domain.

2 summation sign. A i

The corrected signals (G,-) can be composited with respect to frequency by the equation;

calibration operator in the time Where the corrected signals are composited with respect to frequency, the systems calibrations operator for each of the channels can be computed to frequency by the equation:

Q,(/) the system calibration operator in the frequency domain.

with respect Having obtained a systems calibrations operator for each of the channels, any recording at that preselected positioning of the sensing and transmitting elements can be calibrated and a recording having improved accuracy for each channel can be obtained.

Example equations for calibrating a systems signal response are:

T,(r) Hj(t) Qj(t) in the time domain T,(f) [H,-(f)][Q,(f)]in the frequency domain where:

T,(t)= calibrated systems response in the time domain;

T,(f) calibrated systems response in the frequency domain;

H,(t) a systems response represented in the time domain;

H O) a systems response represented in the frequency domain;

Q,(t) the systems calibration operator in the time domain;

Q;(f) the systems calibration operator in the frequency domain;

* convolution j channel number.

By the use of this method, calibration data can be obtained for a recording system in situ. This data can thereafter be applied to recordings obtained at the preselected position for calibrating the recordings, thereby improving the accuracy of the recordings.

What is claimed is:

l. A method for obtaining data for calibrating a recording system in situ, said recording system having a plurality of channels, each having a sensing element, a transmitting element, and a recording element, comprising:

installing the sensing elements and transmitting elements in preselected positions;

controllably exciting each of the sensing elements;

delivering from each sensing element a signal representative of the magnitude of controlled excitation relative to time;

separately receiving and each recording signal;

correcting each said signal in response to the sensitivity of its respective sensing elements;

computing a systems calibration operator for each of the channels.

2. A method, as set forth in claim 1, wherein the sensing elements are geophones, each having a suspended mass, and including biasing the suspended mass of each of the geophones for a preselected period of time; and substantially, simultaneously releasing each mass thereby controllably exciting each geophone.

3. A method, as set forth in claim 2, wherein each mass is biased by passing a static current to each geophone and each mass is released by terminating the current passing to each geophone.

4. A method as set forth in claim 1 additionally comprising compositing each corrected signal for forming a composite signal.

5. A method, as set forth in claim 4, wherein each corrected signal is composited in respect to time by the equation where:

A(t) the composite signal in the time domain;

N the total number of channels;

j a channel number;

Gj(t) corrected signal in time domain.

6. A method as set forth in claim 5, wherein the systems calibration operator for each of the channels is computed with respect to time by the equation where:

Q (t) the system calibration operator in the time domain;

* convolution.

7. A method, as set forth in claim 4, wherein each corrected signal is composited with respect to frequency by the equation Am QM) 61m where:

Q;(f) the system calibration operator in the frequency domain.

9. A method for improving the accuracy of recordings utilizing a recording system having a plurality of channels, each having a sensing element, a transmitting element, and a recording element, comprising:

installing the sensing elements and transmitting elements in preselected positions;

controllably exciting each of the sensing elements;

delivering from each sensing element a signal representative of the magnitude of controlled excitation relative to time;

separately receiving and recording each said signal;

determining from the said signals thus received a systems calibration operator for each of the channels; and

applying said systems calibration operator to a systems response to obtain a calibrated systems response.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNO. 5 D T September 2, 1975 V 1 Harold A. Tims It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, claim 1, line 43, "each recording signal" should read recording each said signal; line 45, after "elements; insert and Signed and Scaled this A new:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner nfPale'nrs and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 2 3,903,505 DATE I September 2, 1975 VENTOR( 1 Harold A. Tims It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, claim 1, line 43, "each recording signal" should read recording each said signal; line 45, after "elements; insert and Signed and Scaled this Arrest.-

RUTH C. MASON C. MARSHALL DANN Alluring Officer Commissioner uflarem: and Trademarks 

1. A method for obtaining data for calibrating a recording system in situ, said recording system having a plurality of channels, each having a sensing element, a transmitting element, and a recording element, comprising: installing the sensing elements and transmitting elements in preselected positions; controllably exciting each of the sensing elements; delivering from each sensing element a signal representative of the magnitude of controlled excitation relative to time; separately receiving and each recording signal; correcting each said signal in response to the sensitivity of its respective sensing elements; computing a systems calibration operator for each of the channels.
 2. A method, as set forth in claim 1, wherein the sensing elements are geophones, each having a suspended mass, and including biasing the suspended mass of each of the geophones for a preselected period of time; and substantially, simultaneously releasing each mass thereby controllably exciting each geophone.
 3. A method, as set forth in claim 2, wherein each mass is biased by passing a static current to each geophone and each mass is released by terminating the current passing to each geophone.
 4. A method as set forth in claim 1 additionally comprising compositing each corrected signal for forming a composite signal.
 5. A method, as set forth in claim 4, wherein each corrected signal is composited in respect to time by the equation
 6. A method as set forth in claim 5, wherein the systems calibration operator for each of the channels is computed with respect to time by the equation Qj(t) A(t)*Gj 1(t) where: Qj(t) the system calibration operator in the time domain; * convolution.
 7. A method, as set forth in claim 4, wherein each corrected signal is composited with respect to frequency by the equation
 8. A method, as set forth in claim 7, wherein the systems calibration operator for each of the channels is cOmputed with respect to frequency by the equation
 9. A method for improving the accuracy of recordings utilizing a recording system having a plurality of channels, each having a sensing element, a transmitting element, and a recording element, comprising: installing the sensing elements and transmitting elements in preselected positions; controllably exciting each of the sensing elements; delivering from each sensing element a signal representative of the magnitude of controlled excitation relative to time; separately receiving and recording each said signal; determining from the said signals thus received a systems calibration operator for each of the channels; and applying said systems calibration operator to a systems response to obtain a calibrated systems response. 